Give an account of the methods used in sequencing the human genome.

Approaches used in human genome sequencing:

There are two methodologies used in sequencing the human genome : Expressed Sequence Tags (ESTs) and Sequence Annotation.

Expressed Sequence Tags (ESTs):

Expressed Sequence Tags (ESTs) is a method in which the genes expressed as mRNA are identified. All the mRNA of the cell is tagged and libraries are formed after converting them into cDNA and being sequenced.

mRNA is the expressed form of a gene and it contains only exons. In this method, the sequence of coding regions of the human genome will be determined.



Sequence annotation:

In the sequence annotation method, all coding and noncoding regions of the DNA are sequenced. The whole genome is sequenced. Later these sequences were assigned with functions.

The sequence obtained is then annotated with the sequence obtained from the coding region in EST to determine the genes and their location.

Sequencing of human genome:

Sequencing of the human genome involves the below mentioned steps:

● Isolation of total DNA from a cell and fragmenting the genome randomly into smaller sizes. The genome is fragmented because there is a technical limitation in sequencing a very long piece of DNA.

● Cloning the fragments in a host using a vector (gene cloning). Gene cloning results in amplification of DNA so that it can be sequenced with ease. The commonly used hosts are bacteria and yeast and the commonly used vectors are BAC (bacterial artificial chromosome) and YAC (yeast artificial chromosome).

● Sequencing. was done by automated sequencers that work based on the technique developed by Fredrick Sanger. These sequences are arranged by the overlapping sequences with the help of a computer.